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How Trees Sleep

Like the rest of us, they droop.

Shhhh, this tree might be sleeping!

Shhhh, this tree might be sleeping! (Photo: Petr Kratochvil/Public Domain)

Have you ever stood under a tree at night, looked up through its criss-cross of branches, and wondered, “What is it up to?”

According to new research, be quiet, because it’s probably catching some z’s. An international team of scientists has found evidence that trees “sleep” at night, their leaves and branches slowly drooping as soon as dusk settles. At about two hours before sunrise, they “wake up” again, gradually returning to their original position.

“The changes are not too large, only up to 10 centimeters,” Eetu Puttonen of the Finnish Geospatial Research Institute told Science Daily. “But they were systematic.”

Even the most casual plant fan could tell you that many flowers close at night, and that some leaves curl up when darkness comes. In the past, experts have studied circadian rhythms in crop seedlings and sunflowers, but experimental constraints have made it difficult to work with anything much larger.

For this study, the researchers used a terrestrial laser scanner to precisely map out a set of points on two separate silver birch trees—one in Austria, and one in Finland. By making a series of these maps between dusk and dawn, and measuring the displacement of each point, they were able to trace how the whole tree moved over the course of the night.

Since the researchers were mostly studying the efficacy of the laser-scanning technology, they didn’t take enough measurements or guarantee a controlled-enough environment to draw wide-reaching conclusions. But their results, published in Frontiers in Plant Science, are still intriguing, and researchers will likely continue bothering trees at night for years to come. Now if we could only figure out what they dream about.

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